Encapsulated modular power converter with symmetric heat distribution

ABSTRACT

A method of encapsulating a panel of electronic components such as power converters reduces wasted printed circuit board area. The panel, which may include a plurality of components, may be cut into one or more individual pieces after encapsulation with the mold forming part of the finished product, e.g. providing heat sink fins or a surface mount solderable surface. Interconnection features provided along boundaries of individual circuits are exposed during the singulation process providing electrical connections to the components without wasting valuable PCB surface area. The molds may include various internal features such as registration features accurately locating the circuit board within the mold cavity, interlocking contours for structural integrity of the singulated module, contours to match component shapes and sizes enhancing heat removal from internal components and reducing the required volume of encapsulant, clearance channels providing safety agency spacing and setbacks for the interconnects. Wide cuts may be made in the molds after encapsulation reducing thermal stresses and reducing the thickness of material to be cut during subsequent singulation. External mold features can include various fin configurations for heat sinks, flat surfaces for surface mounting or soldering, etc. Blank mold panels may be machined to provide some or all of the above features in an on-demand manufacturing system. Connection adapters may be provided to use the modules in vertical or horizontal mounting positions in connector, through-hole, surface-mount solder variations. The interconnects may be plated to provide a connectorized module that may be inserted into a mating connector.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims priority under 35 USC 121to U.S. application Ser. No. 13/105,696, filed on May 11, 2011, nowissued as U.S. Pat. No. 8,966,747. This application is related to U.S.patent application Ser. No. 14/635,420, filed on Mar. 2, 2015, nowissued as U.S. Pat No. 9,439,297.The entire contents of the aboveapplications are herein incorporated by reference.

FIELD OF THE INVENTION

This invention relates to the field of encapsulating electronicassemblies and more particularly to encapsulated power converters.

BACKGROUND

Contemporary electronic power systems require power converters capableof deployment at the point of load. Competing considerations requireincreasing power density, decreasing mounting area on customermotherboard, and lower cost.

An encapsulated electronic module, such as an electronic power convertermodule for example, may comprise a printed circuit assembly over-moldedwith an encapsulant to form some or all of the package and exteriorstructure or surfaces of the module. Encapsulation in this manner mayaid in conducting heat out of the over-molded components, i.e.,components that are mounted on the printed circuit assembly and coveredwith encapsulant. In the case of an electronic power converter module,the printed circuit assembly may include one or more inductivecomponents, such as inductors and transformers. Encapsulated electronicpower converters capable of being surface mount soldered to a customermotherboard are described in Vinciarelli et al., Power Converter Packageand Thermal Management, U.S. Pat. No. 7,361,844, issued Apr. 22, 2008,(the “SAC Package Patent”) (assigned to VLT, inc. of Sunnyvale, Calif.,the entire disclosure of which is incorporated herein by reference).Encapsulated electronic modules having at least one surface of amagnetic core structure exposed and methods for manufacturing the sameare described in Vinciarelli et al., Encapsulation Method and Apparatusfor Electronic Modules, U.S. patent application Ser. No. 12/493,773,filed Jun. 29, 2009, (the “Exposed Core Application”) (assigned to VIChip Inc. of Andover, Mass., the entire disclosure of which isincorporated herein by reference).

Methods of over-molding both sides of a printed circuit board assemblywhile leaving opposing regions on both sides of the printed circuitboard free of encapsulant are described in Saxelby, et al., CircuitEncapsulation Process, U.S. Pat. No. 5,728,600, issued Mar. 17, 1998 andSaxelby, et al., Circuit Encapsulation, U.S. Pat. No. 6,403,009, issuedJun. 11, 2002 (collectively the “Molding Patents”) (both assigned toVLT, Inc. of Sunnyvale, Calif. and incorporated by reference in theirentirety).

Leads for connecting the encapsulated power converter substrate to thecustomer motherboard are described in Vinciarelli et al., SurfaceMounting A Power Converter, U.S. Pat. No. 6,940,013, issued Sep. 6, 2005(the “J-Lead Patent”) (assigned to VLT, Inc. of Sunnyvale, Calif., theentire disclosure of which is incorporated herein by reference).

SUMMARY

In general, in one aspect, a method of making a plurality of electronicdevices is provided. The method includes providing a plurality of moldpanels, which when assembled, form an internal chamber; providing asubstrate having a plurality of conductive traces and a plurality ofcomponents electrically connected to form at least one circuit, thesubstrate having at least one contact for making an electricalconnection to the circuit; forming a panel assembly including the moldpanels assembled with the substrate in the internal chamber and anencapsulant filling spaces between the substrate and interior surfacesof the chamber; curing the encapsulant; and cutting the panel assemblyto expose at least a portion of the at least one contact and form arespective exposed contact.

Implementations of the method may include one or more of the followingfeatures. The cutting can include making a first cut in at least one ofthe mold panels, and in the first cut, making a second narrower cutthrough the panel assembly. The curing can include raising thetemperature of the panel assembly and the first cut is made before thepanel assembly cools after the curing. The cutting can divide the panelassembly producing at least one module having a plurality of layersincluding respective portions of each of the panel molds, the substrate,and the encapsulant, and the module can contain the at least onecircuit. The cutting can define at least one side of the module. Thecutting can defines two or more sides of the module. The method canfurther include treating the exposed contact to protect againstoxidation. Treating the exposed contact can include applying a removableconformal coating to the exposed contact. Treating the exposed contactcan include applying a layer of metal to the exposed contact. The metalapplied to the exposed contact can include solder or a precious metal.Applying a layer of metal can include plating. The method can furtherinclude providing an adapter having at least one electrical terminal;and attaching the at least one electrical terminal to the exposedcontact. The at least one contact can include a plurality of contacts;the module can include a plurality of exposed contacts; the adapter canhave a plurality of electrical terminals arranged to match respectiveones of the plurality of exposed contacts; and the adapter can bemechanically secured to the module. The mold panels can be metal. Therespective portions of the mold panels can provide heat sink surfacesfor the module. Contours can be provided in an internal surface of oneor more of the mold panels. Providing the contours can include matchingdepths of portions of the internal surface to heights of one or moreselected components. The selected components can include at least onemagnetically permeable core and at least one semiconductor device. Thetraces and components can be electrically connected to form a pluralityof separable circuits arranged in a pattern on the substrate; and thecutting can divide the panel assembly along spaces between the separablecircuits into a plurality of modules each containing at least onerespective circuit. The spaces between the separable circuits can havedimensions approximately matching a width of cuts produced by equipmentused to cut the panel assembly. The at least one contact can include aplurality of contacts located in the spaces between the separablecircuits. The plurality of contacts can be formed in the substrate. Theplurality of contacts can be formed and buried below at least onesurface of the substrate. The method can include treating at least oneexterior surface of at least one of the mold panels for solderability.Forming the panel assembly can include dispensing encapsulant into abottom panel mold; assembling the substrate into the bottom panel mold;dispensing encapsulant onto a top of the substrate; and assembling a toppanel mold onto the substrate. The method can include centrifuging theassembly before curing the encapsulant. Forming the panel assembly caninclude assembling the substrate with a first substrate surface facinginto a first panel mold, closing a second panel mold onto the substratecovering a second substrate surface, providing one or more conduits tothe internal chamber, and forcing encapsulant through the one or moreconduits into the chamber. The method can further include centrifugingthe assembly before curing the encapsulant. The method can furtherinclude providing a connector for removably mating with and providingelectrical connection to the metal. The method can further includeproviding a center plate having an opening to accommodate the substrate.Forming a panel assembly can include positioning the substrate in theopening of the center plate and closing the mold panels against thecenter plate. The method can further include providing at least oneopening in the center plate connected to the internal chamber by atleast one conduit; and forcing the encapsulant through the at least oneopening and at least one conduit into the internal chamber. Forming apanel assembly can include securing the mold panels together prior tocuring the encapsulant.

In general, in another aspect, a method of forming an electrical contactis provided. The method includes assembling a panel including asubstrate having one or more conductive features enclosed within thepanel and unexposed to an exterior surface of the panel, the one or moreconductive features being located along a cut line; cutting the panelalong the cut line exposing portions of the one or more conductivefeatures for use as electrical connections to the substrate; andtreating the portions of the one or more conductive features exposedfrom the cutting for preservation as electrical connections.

Implementations of the method may include one or more of the followingfeatures. The treating can include applying solder to the portions ofthe one or more conductive features exposed from the cutting. Thetreating can include applying a conformal coating to the portions of theone or more conductive features exposed from the cutting to protectagainst oxidation. The treating can include applying a metal layer tothe portions of the one or more conductive features exposed from thecutting. The treating can include soldering a lead of an adapter to theportions of the one or more conductive features exposed from thecutting. The method can further include covering at least one surface ofthe substrate in an area including the cut line and the conductivefeatures prior to cutting the substrate. The covering can includeencapsulating the substrate with a molding compound. The method canfurther include providing a registration feature having a predeterminedrelationship to the substrate, and using the registration feature toalign the cutting relative to the cut line. The method can furtherinclude establishing a pattern including at least one conductive layerin the substrate along the cut line to form the conductive features. Thesubstrate can include a multilayer printed circuit board, and thepattern can include a plurality of conductive layers that areestablished along the cut line to form the conductive features. Themethod can further include establishing a pattern including at least oneconductive via in the substrate along the cut line to form theconductive features. The conductive via can be filled with a conductivematerial. The conductive via can be buried in the substrate. Theconductive via can be a through hole contacting the surfaces of thesubstrate. The through hole can be filled with a conductive material.The conductive features can be covered at the surfaces of the substrateby an insulative layer.

In general, in another aspect, an apparatus including a first mold panelis provided. The first mold panel includes an exterior surface, aninterior surface defining an internal cavity, a clamp region located atpoints along a circumference of the internal cavity, and an opening. Thefirst mold panel is adapted to (a) be engaged by pressure in the clampregion, (b) receive in the cavity a circuit panel containing a pluralityof components and mold compound to fill empty spaces in the internalcavity, and (c) be cut after curing of the mold compound.

Implementations of the apparatus may include one or more of thefollowing features. The interior surface in the region of the internalcavity can be adapted to adhere to the mold compound. The apparatus canfurther include a second mold panel. The second mold panel can includean exterior surface, an interior surface, and a clamp region, in whichthe second mold panel can be adapted to (a) close against and mate withthe first mold panel, (b) be engaged by pressure in the clamp region,and (c) be cut after curing of the mold compound. The interior surfaceof the second mold can further define a second internal cavity, theclamp region of the second mold panel can be located at points along acircumference of the second internal cavity, and the internal cavity ofthe first mold panel can be adapted to receive a first side of thecircuit panel and the second internal cavity can be adapted to receive asecond opposite side of the circuit panel. The apparatus can furtherinclude contours formed in the interior surface of at least one of themold panels. The contours can be adapted to match predeterminedcharacteristics of selected ones of the plurality of components. Theinternal surface of the mold panel can be adapted to adhere to themolding compound. The contours can form interlocking features with curedmold compound. One or more of the mold panels can include a non-ferrousmetal, aluminum, or a thermally conductive material. One or more of themold panels can include a non-metallic substance. The apparatus canfurther include at least one channel connected to the internal cavityfor allowing expansion of the mold compound. The apparatus can furtherinclude at least one channel connected to the internal cavity forinjecting mold compound into the internal cavity. The exterior surfaceof the mold panel can include a plurality of fins. The exterior surfaceof the mold panel can include a flat surface. The flat surface can beadapted for a solder joint. The internal cavity can include featuresformed in the interior surface and arranged in a predetermined pattern.The internal cavity can include features formed in the interior surfacealong lines through which the mold panel maybe cut to establish asetback from a cut edge of the mold panel. The mold panel can include atleast one registration feature adapted to engage and establish apredetermined relationship with the circuit panel. One or more selectedportions of the mold panel can be adapted for incorporation into one ormore products, the products being formed by a process which uses themold panel to contain the molding compound. The exterior surface of themold panel can include a flat surface with one or more pins protrudingfrom the flat surface. The exterior surface of the mold panel caninclude a flat surface having one or more holes in the flat surface. Theapparatus can further include a pin inserted into a respective one ofthe one or more holes.

In general, in another aspect, an apparatus including a panel assemblyhaving external surfaces defined by a first mold panel and a second moldpanel is provided. The first and second mold panels form an internalcavity enclosing an internal circuit board, the internal circuit boardhaving a first surface and second surface and a plurality of componentsin an active circuit area on at least one of the surfaces, thecomponents being electrically connected to interconnects containedwithin the internal cavity. The internal cavity is filled with moldcompound in spaces unoccupied by the circuit board and components, andthe panel assembly is adapted to have first selected portions of thefirst and second mold panels cut away to expose the interconnects and tohave second selected portions of the respective mold panels situatednear the active circuit area remain attached to the assembly followingthe cut.

Implementations of the apparatus may include one or more of thefollowing features. The panel assembly can include a clamp regionlocated at points along a circumference of the first and second internalcavities, and the first selected portions can include the clamp region.

In general, in another aspect, an apparatus including a panel assemblyhaving external surfaces defined by a first mold panel and a second moldpanel is provided. The first and second mold panels form an internalcavity enclosing an internal circuit board, the internal circuit boardhaving a first surface and second surface and a plurality of componentselectrically connected to form a plurality of individual circuits, eachindividual circuit being electrically connected to respectiveinterconnects located along a respective circuit perimeter, theinterconnects being contained within the cavity.

Implementations of the apparatus may include one or more of thefollowing features. The panel assembly can be adapted to be cut alongthe circuit perimeter separating the individual circuits, dividing thepanel assembly into individual circuit modules, and exposing selectedportions of the interconnects. The panel assembly can be constructed toretain an integral layered structure after being filled with moldcompound which is subsequently cured, the layered structure comprising afirst layer including a portion of the first mold, a second layerincluding a portion of the mold compound, a third layer including aportion of the circuit board, a fourth layer including a portion of themold compound, and a fifth layer including a portion of the second mold.The internal circuit board can include a plurality of circuits havingthe same functionality. The apparatus can further include one or moreconduits connecting the internal cavity to an external opening. Spacesunoccupied by the circuit board, components, and interconnects in theinternal cavity can be filled with mold compound. The mold compound hasbeen cured. Selected portions of at least one of the mold panels havebeen removed, the selected portions being located near the circuitperimeters.

In general, in another aspect, an apparatus including a modular packageis provided. The modular package has a first external surface, a secondexternal surface opposite the first external surface, and a side wallextending along the perimeter of and connecting with the first andsecond external surfaces. The modular package includes a first layerdefining the first external surface and a second layer defining thesecond external surface, the first and second layers being separated byand in contact with cured mold compound. An electrical circuit islocated between the first and second layers and within the cured moldcompound and including at least one electrical component electricallyconnected to a plurality of interconnects. The side wall includes astrip formed by the first layer, a strip formed by the second layer, anda strip formed by the cured mold compound. The interconnects aredisposed within the side wall.

Implementations of the apparatus may include one or more of thefollowing features. The first and second layers can include anon-ferrous metal or aluminum. The first external surface can include aplurality of fins. The first external surface can include an essentiallyflat area. The essentially flat area can be adapted for a solder joint.The electrical circuit can include a circuit board, and the side wallcan include a strip formed by the circuit board and an additional stripformed by cured mold compound. The interconnects can include conductivefeatures in the circuit board. The circuit board can include amultilayer printed circuit board (“PCB”) and each of the interconnectscan include a plurality of conductive layers in the PCB. Each of theinterconnects can include a plurality of conductive vias in the circuitboard. The apparatus can further include interlocking features. Theinterlocking features can include a contour formed in an interiorsurface of the first layer, the contour being filled with cured moldcompound. The circuit board can include a top surface and a bottomsurface and the at least one electrical component can include a set oftop-side components mounted on the top surface and a set of bottom-sidecomponents mounted on the bottom surface. The top-side components caninclude a number, T, of large-footprint components, the bottom-sidecomponents can include a number, B, of large-footprint components, andthe number T can be approximately equal to the number B. Each of most ofthe top-side large-footprint components can share a respective set ofconductive vias with a corresponding one of the bottom-sidelarge-footprint components. Each of most of the top-side large-footprintcomponents is located in a respective footprint shared by acorresponding one of the bottom-side large-footprint components. Thecircuit board can include a top surface and a bottom surface, the atleast one electrical component can include a number, T, oflarge-footprint components mounted on the top surface, and most of thelarge-footprint components can be distributed symmetrically in relationto an axis on the top surface. The axis can be along a midline of thetop surface. The axis can be defined in relation to a predeterminedcomponent. The apparatus can further include an adapter for providingmechanical and electrical connections between the modular package and anexternal mounting surface, the adapter having a body and a plurality ofelectrical terminals supported by the body; and electrical connectionsformed between the adapter terminals and respective interconnects on themodular package. The adapter body can be mechanically secured to themodular package, and the adapter terminals can be arranged to mate withthe external mounting surface. The external mounting surface can be acircuit board and the terminals can include ends constructed andarranged to be inserted into conductive holes in the circuit board. Theexternal mounting surface can be a circuit board and the terminals caninclude ends constructed and arranged to be surface mount soldered tothe circuit board. The external mounting surface can include a connectorand the terminals can include ends constructed and arranged to mate withthe connector. The interconnects can be disposed along a long edge ofthe modular package, the adapter can be secured to the long edge of themodular package, and the first and second layers of the modular packagecan be oriented perpendicular to the mounting surface. The interconnectscan be disposed along opposite edges of the modular package, the adaptercan be secured to the opposite edges, and the first and second layers ofthe modular package can be oriented essentially parallel to the mountingsurface. The adapter can be constructed and arranged to maintain one ofthe first or second layers in contact with the mounting surface. Theinterconnects can include a surface constructed and arranged forengagement with a connector terminal. The interconnects can include alayer of metal plating.

In general, in another aspect, an apparatus includes a modular packagehaving a first external surface, a second external surface opposite thefirst external surface, and a side wall extending along the perimeter ofand connecting with the first and second external surfaces, the modularpackage including a first layer of metal defining the first externalsurface and a second layer of metal defining the second externalsurface, the first and second layers being separated by and in contactwith cured mold compound; and an electrical circuit for convertingpower, including a printed circuit board (“PCB”), a plurality ofcomponents including semiconductors mounted to the PCB, and a pluralityof interconnects electrically connected to the components, theelectrical circuit being located between the first and second layers andwithin the cured mold compound. The side wall includes a strip formed bythe first layer, a strip formed by the second layer, a strip formed bythe PCB, and one or more strips formed by the cured mold compound. Theinterconnects are disposed within the side wall.

Implementations of the apparatus may include one or more of thefollowing features. The first and second layers can include aluminum,and the first external surface can include a plurality of fins. Thefirst and second layers can include aluminum, and the first externalsurface can include an essentially flat area. The essentially flat areacan be adapted for a solder joint. The PCB can include a top surface anda bottom surface, the semiconductors can include large-footprintswitches. A number, T, of top-side large-footprint switches can bemounted on the top surface, a number, B, of bottom-side large-footprintswitches can be mounted on the bottom surface, and the number T can beapproximately equal to the number B. Each large-footprint switch can beconnected to one or more other components by a respective set ofconductive vias in the PCB, and each of a plurality of the top-sidelarge-footprint switches can share its respective set of conductive viaswith a corresponding one of the bottom-side large-footprint switches.Most of the large-footprint switches can be positioned on one surface ina location substantially overlapping a location on the other surfaceoccupied by another large-footprint switch. The apparatus of claim 151wherein the PCB includes a top surface and a bottom surface, thesemiconductors include large-footprint switches mounted on the topsurface, most of the large-footprint components are distributedsymmetrically between a left side of the top surface and an oppositeright side of the top surface. The PCB can include a top surface and abottom surface, the semiconductors can include large-footprint switchesmounted on the top surface, and most of the large-footprint componentscan be distributed symmetrically between quadrants on the top surface.The components can include a transformer core. The quadrants cansurround the transformer core. The PCB can include a top surface and abottom surface, and the components can include a set of high-profilecomponents having similar heights. A number, T, of the high-profilecomponents can be mounted on the top surface, a number, B, of thehigh-profile components can be mounted on the bottom surface, and thenumber T can be approximately equal to the number B. A spatialdistribution of the high-profile components on the top surface canroughly match a spatial distribution of the high-profile components onthe bottom surface. The apparatus can further include an adapter forproviding mechanical and electrical connections between the modularpackage and an external mounting surface, the adapter having a body anda plurality of electrical terminals supported by the body; andelectrical connections formed between the adapter terminals andrespective interconnects on the modular package. The adapter body can bemechanically secured to the modular package, and the adapter terminalscan be arranged to mate with the external mounting surface. The externalmounting surface can be a circuit board and the terminals can includeends constructed and arranged to be inserted into conductive holes inthe circuit board. The external mounting surface can be a circuit boardand the terminals can include ends constructed and arranged to besurface mount soldered to the circuit board. The external mountingsurface can include a connector and the terminals can include endsconstructed and arranged to mate with the connector. The interconnectscan be disposed along a long edge of the modular package, the adaptercan be secured to the long edge of the modular package, and the firstand second layers of the modular package can be oriented perpendicularto the mounting surface. The interconnects can be disposed alongopposite edges of the modular package, the adapter can be secured to theopposite edges, and the first and second layers of the modular packagecan be oriented essentially parallel to the mounting surface. Theadapter can be constructed and arranged to maintain one of the first orsecond layers in contact with the mounting surface. The interconnectscan include a surface constructed and arranged for engagement with aconnector terminal. The interconnects can include a layer of metalplating. The first layer can include contours formed in an interiorsurface of the first layer, the contours including a first featurehaving a shape and an elevation to accommodate a first component on thePCB, the first component having a height greater than or less than othercomponents on the PCB. The first component can include a magnetic corestructure and the elevation can be a recess in the interior surface. Thefirst component can include a semiconductor switch and the elevation canbe a protrusion from the interior surface. The apparatus can furtherinclude interlocking features having a contour formed in an interiorsurface of the first layer, the contour being filled with cured moldcompound. The modular package can include a recess formed in the firstlayer adjacent one or more of the interconnects providing a setbackbetween the first layer and the one or more interconnects.

In general, in another aspect, an apparatus includes a power converteris provided. The power converter includes a printed circuit board(“PCB”) having a plurality of conductive layers and having a top surfaceand a bottom surface; a magnetic core structure magnetically coupled toa winding formed by traces in one or more of the conductive layers inthe PCB; and a plurality of power semiconductor devices. A first set ofthe power semiconductor devices is mounted on the top surface andelectrically connected to dissipate power at a level, Pt, duringoperation of the converter, and a second set of the power semiconductordevices is mounted on the bottom surface and electrically connected todissipate power at a level, Pb, during operation of the converter. Thepower semiconductor devices are distributed between the first and secondsets to distribute heat generation during operation of the convertersuch that each level Pt, Pb is less than 150% of the other level Pb, Pt.

Implementations of the apparatus may include one or more of thefollowing features. A plurality of the power semiconductor devices inthe first set can each be positioned in a location on the top surfacesubstantially overlapping a location on the bottom surface occupied by apower semiconductor device in the second set. The power semiconductordevices can be electrically connected using a respective set ofconductive vias in the PCB, and a plurality of the power semiconductordevices in the first set can share their respective sets of conductivevias with corresponding power semiconductor devices in the second set.The power converter can include circuitry having a pair of cells thathave a common circuit topology and each including power semiconductorswitches from each of the first and second sets. Each cell can have itsrespective components arranged in a pattern, in which the pattern ofcomponents of one cell is substantially a mirror image of the pattern ofcomponents in the other cell. A component from one of the cells can belocated on an opposite surface of a respective component from the otherone of the cells. The cells can include input cells. The powersemiconductor devices can include output switches.

In general, in another aspect, a method of manufacturing a plurality ofproducts is provided. The method includes inserting a plurality ofcomponents into a cavity formed by one or more molds; closing the one ormore molds to form a seal around the cavity; filling the cavity withmold compound; curing the mold compound in the cavity to secure thecomponents, cured mold compound, and molds together into an assembly;and cutting the assembly to separate the plurality of products from theassembly, the products each including a respective section of the one ormore molds which remains as an integral part of each respective product.

Implementations of the method may include one or more of the followingfeatures. The method can further include maintaining a predeterminedalignment between the plurality of components and the one or more molds.The plurality of components can include a substrate having conductivefeatures. The cutting can include exposing portions of the conductivefeatures in each respective product.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 shows an electronic module 100.

FIG. 2 shows a panel assembly 120 comprising a plurality of electronicmodules before singulation.

FIG. 3 shows an exploded view of the panel assembly revealing the heatsink panels 121 and 122 and internal PCB panel 124.

FIG. 4 shows the panel assembly 120 with the top heat sink panel 121removed.

FIG. 4A shows an exploded view of the PCB panel and lower heat sinkpanel in a modified panel assembly 120.

FIG. 4B shows a cross-section of the panel assembly 120A along lines4B-4B in FIG. 4A.

FIG. 5 shows a plan view of the PCB panel 124 assembled with the bottomheat sink panel 122.

FIG. 6 shows a cross-section of the panel assembly 120.

FIG. 7 shows a partial cross section of the panel assembly closed in amold.

FIG. 8 shows another partial cross section of the panel assembly closedin a mold.

FIG. 9A shows a plan view of the panel assembly 120 followingsingulation.

FIGS. 9B, 9C show optional channels formed in the panel beforesingulation.

FIGS. 10A, 10B show single modules 115, 115B after singulation.

FIG. 11 shows an enlarged portion of the module 115 revealing details ofexposed buried-embedded interconnects.

FIG. 12 shows a cross section of the singulated module 115 of FIG. 10A.

FIG. 13 shows a connector assembly.

FIG. 14 shows an exploded view of the connector assembly.

FIG. 15 shows a horizontal through-hole mount module 200.

FIG. 16 shows an exploded view of the through-hole mount module 200.

FIG. 17 shows a horizontal surface-mount module 300.

FIG. 18 shows an exploded view of the surface-mount module 300.

FIG. 19 shows an alternative horizontal surface-mount module 400.

FIG. 20 shows a top view of the surface-mount module 400.

FIG. 21 shows an exploded top view of module-connector set 500.

FIG. 22 shows an exploded view of the connector set 503.

FIG. 23 shows an exploded bottom view of module-connector set 500.

FIG. 24 shows an isometric view of the module-connector set 500assembled.

FIG. 25 shows an alternative horizontal through-hole flush-mount module600 exploded from a customer PCB.

FIG. 25A shows an alternative horizontal through-hole flush-mount module650 exploded from a customer PCB.

FIG. 26 shows the horizontal through-hole flush-mount module 600assembled onto a customer PCB.

FIG. 27 shows top and bottom plan views of a section of a PCBillustrating symmetry of component layouts.

FIG. 28 shows an exploded perspective view of a panel assembly 720including a manifold plate.

FIG. 29 is an exploded side view of the panel assembly 720 showing thePCB mated with the manifold plate.

FIG. 30 shows a top plan view of the panel assembly 720.

FIG. 31 shows a top plan view of the panel assembly 720 with the topheat sink panel removed.

FIG. 32 shows a side view of the panel assembly 720 closed in a mold.

Like references symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

I. Vertical PCB Package.

Referring to FIG. 1, an electronic module 100, e.g. a power converter,is shown having a generally rectangular form factor with two large faces114A, 114B covered by heat sinks 101, 102. As shown between the heatsinks 101 and 102, the module 100 includes a printed circuit board(“PCB”) 104 having its large faces arranged generally coplanar to thetwo large faces 114A, 114B of the electronic module 100. Electroniccomponents (FIGS. 3, 5, 6) may be mounted to one or both sides of thePCB 104 and electrically interconnected, e.g. by conductive traces on orin the PCB 104 to form the module circuitry. Using a power converter asan example, the electronic components may include power transistors,control ICs, and discrete resistors and capacitors. One or more magneticcore structures may be provided, which in combination with conductivetraces on PCB 104, may form planar magnetic components such as inductorsand transformers.

The electronic components may protrude from one or both sides of the PCB104 to varying degrees depending upon component size. Spaces between thefaces of PCB 104 and the components on the PCB on one hand and theinterior surfaces of the heat sinks on the other hand may be filled withmolding compound, which when cured may form integral structural layers105, 106 as shown in FIG. 1 and further provides a thermally conductivemedium in which heat may be readily conducted away from the PCB andcomponents to the heat sinks 101, 102. The interior surfaces of the heatsinks may be contoured to match the height of one or more of thecomponents while maintaining an appropriate clearance for insulation andsafety agency requirements. Contouring the heat sinks 101, 102 in thisway: (1) to match the height of the magnetic core structure may be usedas an alternate approach to the exposed core encapsulation methoddescribed in Vinciarelli, Encapsulation Method and Apparatus forElectronic Modules, U.S. patent application Ser. No. 12/493,773 filedJun. 29, 2009 (assigned to VI Chip Corp. of Andover, Mass., the entiredisclosure of which is incorporated herein by reference); (2) to matchthe height of lower profile components, such as power semiconductors,may (a) increase thermal performance in the case of heat dissipatingcomponents by replacing molding compound with heat sink metal; and (b)reduce cost generally by reducing the volume of molding compoundrequired; and (c) further reduce cost by allowing less expensive moldingcompound to be used because of reduced thermal pathways through theencapsulant, easing the thermal conductivity requirements of theencapsulant (e.g., an encapsulant having a 1 degree Celsius per wattthermal resistance may be used with the contoured heat sink instead ofan encapsulant having a 3 degrees Celsius per watt thermal resistanceused without the contoured heat sink).

A connector 103, including terminals 108, 109, 110 and standoffs 107,may be provided as shown along an edge of the PCB 104 to make electricalconnections between the electronic module 100 and external circuitry. Asshown in FIG. 1 with the connector 103 situated along one edge of themodule 100, preferably one of the longest edges, the module 100 may bemounted vertically, i.e. with its internal PCB 104 perpendicular to achassis or another circuit board such as a motherboard. Using thevertical mount module construction illustrated in FIG. 1 for a powerconverter may provide advantages over the more conventional horizontalmounting technique. For example, using the vertical PCB arrangement mayallow use of a magnetic core structure that is thicker than in ahorizontal PCB configuration, e.g. because of height restrictions,enabling increased power throughput, as compared to a similar converterusing a horizontal PCB orientation. The length of the magnetic path maybe also reduced in the vertical PCB configuration further reducinglosses in the magnetic components. Shorter windings may also be usedfurther reducing transformer or inductor losses. Further details andvariations of, and a process for making, the electronic module will bediscussed below in connection with a panel molding process.

II. Panel Molding Process.

A. Overview

The electronic module 100 shown in FIG. 1 may be fabricated using apanel molding process described with reference to FIGS. 2-9. The panelmolding process may be used to produce a multiplicity of modules at atime. A PCB panel 124 may be provided with a plurality of individualcircuits for building the electronic modules. FIGS. 3, 4, and 5 show thePCB panel 124 populated with electronic components revealing a 3-by-4pattern of twelve circuits to make twelve individual modules 115(labeled 115A through 115L in FIG. 5). The illustrative example of FIGS.3-5, being for power converters, includes magnetic core structures 131(FIG. 3) in addition to electronic components 132. As shown in FIG. 5,the pattern of individual circuits 115A-115L are arranged close togetherand separated by small spaces 135 preferably sufficient to allow the PCBpanel to be cut during the singulation process without necessitating twocuts between modules or unnecessary waste of PCB material. The spacingmay be adjusted based upon the cut dimensions produced by the equipmentused to make the cuts.

The PCB panel 124 containing the multiplicity of the electronic circuits(115A-115L in FIG. 5) may be assembled with matching heat sink panels121, 122 as shown in FIG. 3 to form a panel assembly 120 (FIG. 2). Asshown in FIGS. 3 and 6, the two heat sink panels 121 and 122 whenassembled together may form an internal cavity 146, which completelyencloses the populated PCB panel 124. FIGS. 2 and 6 show that the heatsink panels 121 and 122 may be pressed together (e.g. by a mold press161, 162 as shown in FIG. 7) to form a seal 123 (FIGS. 2, 6-8) aroundthe perimeter of the internal cavity 146. In this example, the heat sinkpanels 121 and 122 also function as mold panels by forming a mold cavity(e.g., the internal cavity 146) that may be filled at least in part byan encapsulant encapsulating the surfaces of the PCB panel 124 and theelectronic components on the PCB panel 124.

B. Heat Sink Panels

Referring to FIG. 2, the heat sink panels 121, 122 may include fins onthe exterior surfaces as shown. The fins may be arranged in anydirection relative to the panel or in any pattern and may vary inheight, thickness, and spacing as required for the particularapplication. For example, modules 115 and 115B shown in FIGS. 10A and10B respectively illustrate longitudinal and transverse finorientations. Alternatively, one or both of the heat sink panels mayhave a generally flat exterior surface omitting the fins altogether. Forexample, FIGS. 17 and 25 show modules 315 and 615 produced when bothheat sink panel exterior surfaces are flat and one is flat and one isfinned, respectively. The thickness of the panels between the internalcavity and the external surface may be varied to suit the particularrequirements of the application.

C. Heat Sink Internal Contours

Referring to FIG. 3, the contoured interior surface of the bottom heatsink panel 122 is shown including a 3-by-4 repeating pattern of twelve(A through L) prominent recesses 141 and shallower recesses 142 and 143.Recesses 141 may be matched to the downward protruding portion ofmagnetic core structures 131. Similarly, recesses 142 and 143 may bematched to other downwardly protruding components on the PCB panel 124.Note that in the example of FIG. 3, because the core structure 131protrudes from the PCB 124 more than the other components, the recesses141 are deeper than recesses 142, 143. Although not visible in FIG. 3,the interior surface of heat sink panel 121 may similarly includecontour features to match the components and core structure on theupward facing side of the PCB panel 124 (e.g. as shown in thecross-section of FIGS. 6, 7). Although the interior contour of panel 122in FIG. 3 is shown including three recesses 141, 142, 143 repeated foreach circuit (A through L in the 3-by-4 pattern), the interior contoursof the heat sink panels 121 and 122 may range from simple flat surfaces(accommodating the height of the tallest component) to a complexarrangement of a multiplicity of recessed and protruding features(accommodating a multiplicity of component heights) which at the extremecould match every component individually.

Additional features may be provided in the heat sink panels tofacilitate the panel molding process, to enhance the mechanicalintegrity or performance of the finished module 100, or to satisfysafety agency clearance requirements for the finished product. By way ofexample undercut features, such as undercuts 148 shown in FIGS. 6, 7,and 12 may be provided at each circuit site (i.e. within each individualmodule location) in the heat sink panels 121, 122. As shown theundercuts 148 may be provided in selected recesses, such as recesses143-1 and 143-2, and may be dispersed along one or more of the boundarylines of each circuit 115. During encapsulation, molding compound fillsthe recesses and trenches and their respective undercuts 148. Whencured, the hardened molding compound in the undercuts forms adovetail-like joint securing the heat sinks to the encapsulated PCB 124.When provided at each circuit site, the undercuts secure the heat sinks101, 102 to the PCB 104 in the individual module 115 providingmechanical integrity after singulation. Referring to the cross-sectionof a singulated module 115 in FIG. 12, dovetail interfaces 149-2 and149-1 are shown securing the top and bottom heat sinks 101, 102 to theencapsulated PCB assembly.

Additionally, clearance features may be provided in the heat sink panelsto satisfy minimum safety agency clearances between electrical contactson the PCB 124 and the metal heat sinks 121, 122. As shown in FIGS. 6and 7, trenches 147 may be provided in heat sink panels 121 and 122along the side of each module 115 (the long side as shown in FIGS. 6 and7) where electrical contacts (discussed in more detail below) areexposed in or on the PCB 124. The trenches 147 may also include theundercut features 148 discussed above. For example, cut trench 147 inFIG. 12 results in a recess 150 of the heat sink 101 away from the edge104E of the PCB 104 after singulation.

D. PCB-Heat Sink Registration

Registration features may be provided in one or both of the heat sinkpanels 121, 122 helping to correctly position the PCB panel 124 in thecavity 146 relative to the heat sink panels 121, 122 (which isparticularly important when the panel is cut during the singulationprocess) and to correctly position the heat sink panels relative to eachother during assembly and during subsequent molding processes. Referringto FIGS. 3 and 4, beveled corners 144 may be provided in heat sink panel122 to interface with matching indentations 133 which may be provided inPCB panel 124 for registration when assembled together (FIGS. 4 and 5).FIG. 5, which is a top plan view of the PCB panel 124 assembled with thebottom heat sink 122, shows the beveled corners 144 interfacing with theindentations 133.

Referring to FIG. 4A, a modified version of the assembly is shown. Asshown, a registration pin 151 is press fit into a registration hole 152in the lower heat sink panel 122 and a matching registration hole 134 isprovided in the PCB panel 124. The completed panel assembly, includingthe lower heat sink panel 122, PCB panel 124, and upper heat sink panel121, is shown in FIG. 4B in cross-section taken along the broken lines4B-4B in FIG. 4A. As shown in FIG. 4B, the registration pin 151, whichfits snugly in registration holes 152 and 134, provides registration forthe PCB panel 124 relative to the lower heat sink panel 122. Anindentation 153 may be provided in the opposite heat sink panel (121) toaccommodate protrusion of the pin 151 past the PCB 124. As showngenerally at 154 in FIG. 4B, the heat sink panels may include additionalfeatures to provide registration between the top and bottom heat sinkpanels. Although a registration pin is shown at one corner of the panel122 in FIG. 4A, it will be appreciated that additional pins may be usedat other locations. For example, FIG. 4 shows two registration holes134, one on a corner and another in the middle of the opposite side ofthe PCB panel 124.

E. Encapsulation

FIG. 6 shows a cross-sectional view (through lines 6-6 in FIG. 5) of thepanel 120 through an opening 125 and a conduit 145 in the heat sinkpanels. The openings 125, which may be slot shaped as shown (FIGS. 2, 3,4, 5, 9), may be connected to the interior cavity 146 of the panelassembly 120 by conduits 145 for conveying molding compound or ventingduring the panel molding process. The openings may be formed in one ofthe heat sink panels, e.g. openings 125 in the top heat sink panel 121as shown in FIGS. 2, 3, 4, 5, and 9, or in both heat sink panels, e.g.openings 125B in the top and bottom heat sink panels 121, 122 as shownin FIGS. 6 and 7. Referring to FIG. 6, the conduits 145 may be formed byrecesses in the interior surfaces of heat sink panels 121 and 122,connecting the openings 125 to the interior cavity 146. The recessesforming the conduit 145 may be situated near the edge 124C of PCB panel124 to allow the molding compound to flow over both top 124A and bottom124B surfaces of the PCB 124.

FIG. 7 shows an enlarged cross-section of one end of the panel assembly120 closed between an upper mold press 161 and lower mold press 162taken through some of the smaller components, e.g. components 132-1,132-2, i.e. through lines 6-6 in FIG. 5. A channel 163 may be provided,e.g. between the upper mold press 161 and lower mold press 162 as shown,to interface with openings 125. Molding compound may be forced throughthe channel 163 under pressure after the panel assembly 120 is closed inthe mold presses 161, 162. The dashed line 167 with directional arrowsin FIGS. 7 and 8 illustrates the flow of molding compound through thechannel 163 into openings 125 through conduits 145 over the top 124A andbottom 124B surfaces of the PCB panel 124 during encapsulation. Themolding compound may be forced into the internal cavity 146 to fill allof the unoccupied spaces between the heat sinks 121, 122 and the PCBpanel 124.

FIG. 8 shows an enlarged cross-section of one end of the panel assembly120 closed between an upper mold press 161 and lower mold press 162taken through the magnetic core structures, i.e. through lines 8-8 inFIG. 5. Each magnetic core 131 is shown having an upper E-core 131-2 anda lower E-core 131-1 separated by a gap 131-3. The cores have openings131-4 to accommodate windings formed on the PCB 124. As shown, the lowercore 131-1 and upper core 131-2 are accommodated by recesses 141-1 and141-2 in the lower heat sink 122 and upper heat sink 121, respectively.As shown, compliant pads 136 may be provided on the surfaces of thecores 131-1 and 131-2 or in recesses 141-1, 141-2 to accommodatedimensional differences in the components. The compliant pads may bechosen for good thermal conduction and optionally adhesive propertiesfacilitating heat removal from the cores into the heat sink whileoptionally providing structural integrity to the assembly. Gap Pad A2000available from the Bergquist Company, 18930 West 78th St, Chanhassen,Minn 55317 is one example of the type of compliant pad that may be used.Alternatively and perhaps depending upon the tolerances involved, aphase change material may accommodate the dimensional difference duringassembly and when cured afterward provide structural integrity betweenthe heat sinks and the cores.

Molding compound may be deposited in one or more of the recesses, e.g.recesses 141-1 or 141-2, in the internal cavity prior to assembly of thePCB panel 124 into one or both of the heat sink panels 121, 122 toensure that the molding compound fills narrow spaces between the heatsink and the components, e.g. the cores 131-1, 131-2. One or more ventopenings (not shown) may be provided in the heat sink panels, preferablyat an end opposite the fill openings 125, to allow the molding compoundto flow completely through the internal cavity 146. The cavity may befilled with encapsulant either (1) by transfer through one or moreconduits, (2) by measured deposition of encapsulant during assembly ofthe panels, or (3) by both measured deposition during assembly andtransfer through conduits.

As shown in FIGS. 4, 5, and 6, the border areas between the modules andaround the periphery of the PCB panel 124 may be minimized to avoidwasted PCB material. Because the heat sink panels 121 and 122 closeagainst each other rather than the PCB panel 124, areas on the PCBnormally reserved for closing the mold may be eliminated furtherreducing PCB waste and thus overall cost.

After the panels are assembled together and the interior cavities arefilled with molding compound, the panel assembly 120 may be cured, e.g.by elevating the temperature.

F. Singulation

Singulation is the process by which individual modules, e.g. singulatedmodule 115 in FIG. 10A, are separated from the panel assembly 120, e.g.by cutting. The panel assembly 120 may be singulated after the moldingcompound is cured. The panel assembly 120 is separated from the upperand lower mold presses 161, 162 and may be cut, e.g. along lines 128,129 as shown in FIG. 9A, to singulate the modules 115A-115L. Forexample, a narrow saw may be used to cut through the layers (e.g. asshown in FIGS. 1, 10A, 10B, 12) of panel 120, which may include heatsink 101, cured molding compound 105, PCB 104, cured molding compound106, and heat sink panel 102. For example, a 0.025 inch thick saw suchas model number EAD-3350 available from Disco Corp., Ota-ku, Tokyo,Japan may be used. Referring to the cross-sectional views of FIGS. 6 and7, dashed lines 129 illustrate the lines along which the panel 120 maybe cut to singulate modules 115D, 115E, and 115F. As shown, the cuts 129(along the long side of the individual modules 115) go through themiddle of the trenches 147. The trenches 147 may be made wide enough andthe cuts 129 may be made at an appropriate distance from the edges ofthe trench 147 to ensure that a minimum thickness of cured moldingcompound remains in the trench after singulation to be mechanicallyrobust. The trenches 147 may also be used to reduce the thickness ofmetal through which the saw must cut during singulation, e.g. byoptionally providing trenches along the perimeter of each module.

G. Electrical Connections

Interconnection features may be embedded in the PCB panel 124,preferably along the boundaries of the individual circuits, so thatelectrical contacts are at least in part formed by or exposed duringsingulation. To maximize the area on a PCB panel 124 available forcircuitry, the interconnection features may preferably be buried in thePCB panel 124 below the top and bottom surface layers. For example, theinterconnection features may be formed in the inner conductive layersbut not occupying valuable area on the surface conductive layers,potentially reducing setback and other spacing requirements. Theinterconnect features therefore are preferably formed in the PCB panel124 before the panel 120 is assembled and exposed when the panels arecut, e.g. during singulation. The interconnection features may comprisea pattern of conductive layers or buried vias (frequently used to formconnections between internal conductive layers) or both in the PCBsituated along the circuit boundary, i.e. lying in the cut line, e.g.cut line 129 (FIG. 9A).

Referring to FIG. 10A, a module 115 is shown after singulation. Exposedinterconnects 111, 112, and 113 are shown embedded in the edge of thePCB 104 along one of the edges 116 of the module 115. As shown in FIG.10A, longer connections 111 and 113 provide greater interconnect surfacearea and higher current carrying capacity, making them amenable for useas power connections, than shorter connections 112 which have lessinterconnect area and lower current carrying capacity, making themuseful for control signal connections. FIG. 11 shows an enlarged view ofa portion of the module 115 along edge 116 revealing detail of the twointerconnections 111 after singulation. The width along the boundary andnumber of the conductive features arranged vertically through the PCBlayers may be adjusted to provide the requisite contact area for eachconnection. In the example of FIG. 11, conductive features, e.g.conductive lands 111A through 111L, formed along the cut line on aplurality of the conductive layers of the PCB form a stack of conductivestrips resembling a bar code after singulation. The stack of conductivelands may provide more contact area than possible with a single buriedvia. In FIG. 11, each interconnect 111 is made up of twelve lands, eachland being formed on a respective one of twelve inner conductive layers.Note that FIG. 11 shows the twelve lands (111A through 111L) buriedbelow the top 124A and bottom 124B surfaces of the PCB, i.e. notoccupying surface area on those layers. During singulation, the saw cutsthrough the buried embedded lands, exposing the edges of the remainingconductive material forming the interconnects 111A through 111L shown inFIG. 11. Note that the buried embedded lands may be shared between twoadjacent modules 115 on the panel 120, e.g. where the PCB patterns arelaid out in mirror image to each other, allowing the modules to be laidout on the PCB panel close to a singulation cut width apart. Also, theinterconnect features may be aligned along a single module boundary asshown or may occupy two or more boundaries of each individual module inthe panel. The exposed edges may then be used to form electricalconnections immediately after singulation, i.e. before the cutinterconnects oxidize or may be protected against oxidation, e.g. with aconformal coating, such as an organic solderability preservative(“OSP”), applied after singulation, to ensure subsequent ability to formelectrical connections to the edges. For example, Entek Plus HTavailable from Enthone, Inc., a Division of Cookson Electronics, WestHaven, Conn. 06516 may be used as an OSP to protect the interconnects.

The number of lands, i.e. conductive layers, used to form eachinterconnect may be increased for better electrical connections orreduced for less critical connections. Although embedded conductivelands are shown in the example of FIGS. 10A, 11, additional oralternative conductive features may be used to form the interconnects.For example, buried conductive vias located along the cut line may beused, either alone or in combination with the lands. The buried vias maybe located so that the singulation cut leaves the walls of theconductive vias exposed resulting in vertical conductive strips, i.e.generally perpendicular to the PCB top and bottom surfaces 124A, 124B,in the PCB edge. Buried conductive vias may tend to fill with adhesiveduring fabrication of the PCB panel 124. Empty conductive vias, i.e.free of non-conductive adhesives, may be preferable for the resultingconcave conductive features, i.e. embedded conductive half cylinders.Similarly, solid buried conductive vias or conductive vias filled withconductive material during the PCB manufacturing process may bepreferable for the resulting continuous flat conductive surface.

In the alternative to buried conductive features, conductivethrough-holes, which are generally free of adhesives followingfabrication of the PCB panel 124 may be used along the cut line to forminterconnects extending through the thickness of the PCB from topsurface to bottom surface providing generally half-cylindricalinterconnects. A penalty of using through-holes for the interconnects isthe loss of surface area on the top and bottom of the PCB which mayotherwise be used for setback or other safety and agency approvalrequirements. Preferably, the through-holes may be filled, for examplewith a conductive material such as solder or silver paste, or conductivepins may be inserted into through holes and soldered to the throughholes, to prevent molding compound from filling the through hole duringthe encapsulation process and to provide a greater contact surface areayielding generally flat conductive interconnects following singulation.

The exposed interconnect features, e.g. 111A through 111L may be used tomake a variety of electrical connections. For example, the exposedinterconnects may be solder plated and then subsequently soldered to amotherboard, e.g. using surface mount soldering techniques. Theinterconnects may be soldered to a connector, such as connector 103shown in FIGS. 1, 13, 14. Alternatively, a lead frame or PCB may besoldered to the exposed interconnects 111, 112, 113 of the modulequickly after singulation. Yet another alternative includes a preciousmetal such as gold or silver or other suitable conductive materialdeposited to the exposed contacts, e.g. by plating, to build up thecontacts into a larger area, e.g. continuous conductive contacts, wellsuited to connectorized modules described in more detail below.

G1. Vertical Mount Connector

Referring to FIGS. 1, 13 and 14, a connector 103 suitable for attachmentto the edge 116 of the module 115 is shown having a connector body 118with a plurality of recesses 117 and a plurality of holes 119A, 119B,and 119C. A plurality of connector pins 108, 109, 110 may be insertedinto holes 119A, 119B, 119C, respectively, from the top 118A. As shown,the holes may be contoured to provide a pressure fit having a grippingforce suitable for retaining the pins. The broad top surfaces 108A,109A, 110A of the pins are suitable for making solder connections to theexposed interconnects 111, 113, 112, respectively on the edge 116 of thePCB 104 of module 115. As shown, the recesses 117 provide countersinkingfor the top portions of the pins allowing the connector body to mountflush to the edge 116 of module 115 and allowing space for a solderjoint between the pin and the respective interconnect. Theinterconnection features may preferably be provided along a long edge ofthe module 115 yielding a more stable vertical mount module 100 such asshown in FIG. 1. However, the interconnection features may be deployedalong any or all of the edges of the module 115 for different mountingconfigurations as discussed more fully below.

G2. Horizontal Through-Hole Mount

Referring to FIGS. 15 and 16, a horizontal mount component 200 suitablefor through hole mounting in a motherboard is shown including asingulated module 215 and through-hole adapters 203A, 203B. Thehorizontal mount module 200 may be constructed in the same manner asdescribed above for the module 100, except that the interconnects arepreferably disposed along two edges of the module PCB and connectorsadapted for horizontal mounting may be used. As shown in FIG. 16, theinterconnects are disposed along the two shorter edges of the PCB 204 inmodule 215. However, the longer edges may be used instead of, or inaddition to, the shorter edges for the interconnects. Although only oneset of the interconnects 211, 212 is visible in the perspective view ofFIG. 16, it will be understood that a second set, including twoadditional power interconnects, is disposed along the opposite hiddenedge of the PCB.

Through-hole adapters 203A and 203B, suitable for attachment to theedges of the singulated module 215 are shown having adapter bodies 218supporting conductive terminals 208, 210 and 209, respectively. Aportion of each terminal may be exposed on an internal surface via anopening in the adapter body optionally providing a small recess. In FIG.16 for example, adapter 203B is shown having two power terminals 209,each having an exposed areas 209A recessed in openings in surface 218Aof the adapter body 218. The exposed areas 209A align with theirrespective interconnects when the adapters 203A, 203B are assembled ontothe module 215. The recesses provide countersinking for the exposedterminals allowing the internal surface 218A of the adapter body 218 tomount flush to the edge of module 215 and allowing space for a solderjoint between the terminal and the respective interconnect. The adapterbody 218 may include a flange 218B which may form a pressure fit withthe adjacent edges of the modules 25. Additional features may beprovided for maintaining the structural integrity of the module andconnectors.

As shown in FIG. 16, epoxy may be deposited along an internal edge ofthe connector body, e.g. in the shaded area 219 preferably aligned withthe encapsulant layer 206 to secure the adapters 203A, 203B to themodule 215. The horizontal mount module 200 may be readily adapted tomatch industry standard brick footprints for power converters, inparticular the module 200 may fit within the standard ⅛^(th) brickfootprint.

G3. Horizontal Surface-Mount

Referring to FIGS. 17 and 18, a horizontal-mount component 300 suitablefor surface-mount soldering to a motherboard is shown including asingulated module 315 and surface-mount adapters 303A and 303B. Thehorizontal-mount module 300 may be constructed in the same manner asdescribed above for the module 200 (FIGS. 15, 16) substituting surfacemount adapters 303A, 303B for through-hole adapters 203A, 203B. As shownin FIG. 17, the singulated module 315 may have flat heat sinks 301, 302instead of the finned heat sinks (shown in FIGS. 1-4, 6-12, 15-16).Although shown disposed along the two shorter edges in FIGS. 17 and 18,the interconnects may be deployed along the longer edges of the PCB 304in the singulated module 315 instead of, or in addition to, the longeredges.

In FIGS. 17 and 18, the surface-mount adapters are shown with smallerbodies 318 than the through-hole adapters (218: FIG. 15, 16) exposingthe connections between the terminals and their respective interconnectsduring assembly and for post assembly inspection. The terminals 308,309, 310 each may include a portion, e.g. solder pads 308A, 310A, 309A,adapted for connection, such as a solder joint, to a respectiveinterconnect on the module, e.g. interconnect 311, 312, and 313 (notvisible in FIGS. 17 and 18). Holes 308B, 309B, 310B may be provided insolder pads 308A, 309A, 310A for better solder joints. Each terminal308, 309, 310 may include a bend (e.g. 308C) to produce a surface-mountpad (e.g. 308D) for attachment, e.g. by surface-mount soldering, to acustomer motherboard.

The adapter bodies 318 may include flanges 318B, preferably along two ormore sides to form a pressure fit with the adjacent edges of the modules315. Additional features may be provided for maintaining the structuralintegrity of the module and adapters. As shown in FIG. 18, epoxy may bedeposited along an internal edge of the connector body, e.g. in theshaded area 319 preferably aligned with the encapsulant layer 306 tosecure the adapters 303A, 303B to the module 315.

G4. Surface-Mount Lead Frame

An alternate embodiment of a horizontal-mount component 400 suitable forsurface-mount soldering to a motherboard is shown in FIGS. 19 and 20including a singulated module 415. The horizontal-mount module 400 maybe constructed in the same manner as described above for the module 300(FIGS. 17, 18) substituting lead frame adapter 403 for the surface-mountadapters 303A, 303B. Like module 315 (FIG. 17), the singulated module415 may have flat heat sinks 301, 302 instead of the finned heat sinksof the previous examples. However, in the example of FIGS. 19 and 20,the interconnects are shown deployed along the longer sides of thesingulated module 415. However, as noted above the interconnects may bedeployed along any edges of the PCB 404 as desired in the singulatedmodule 415.

The surface-mount adapter is shown in FIGS. 19 and 20 having a unitaryrectangular frame-like body 418 supporting a plurality of terminals 408.The profile of the frame body 418 may as shown leave a portion of theterminals exposed for making connections to their respectiveinterconnects during assembly and for post assembly inspection. Theterminals 408 each may include a portion, e.g. solder pad 408A, adaptedfor connection, such as a solder joint, to a respective interconnect onthe module (not visible in FIGS. 19, 20). Although shown without holesin FIG. 19, the solder pads may optionally include holes such as thoseshown in FIGS. 17 and 18. Each terminal 408 may include a bend (e.g.408C) to produce a surface-mount pad (e.g. 408D) for attachment, e.g. bysurface-mount soldering, to a customer motherboard.

The opening in the frame body 418 may be sized to accommodate theperimeter edges of the singulated module 415 and optionally form apressure fit. The frame body 418 may include recesses 417 foraccommodating the terminals 408, allowing the interior surface 418A ofthe frame body 418 to rest flush against the module 415 surface.Additional features may be provided for maintaining the structuralintegrity of the module and adapters. Gaps may be provided in theinterior surface 418A to allow the application of epoxy to secure theframe body 418 to the module 415.

G5. Connectorized Module

The modules 100, 200, 300, and 400 discussed above in connection withFIGS. 1, and 15-20 are all examples in which connectors or adapters aremechanically and electrically connected to the interconnects on thesingulated modules forming an integral modular component. Yet anotheroption is to adapt the module to be removably mated with a connectorthat may be mounted on a customer circuit board. For example, the moduleinterconnects may be plated up with an appropriate conductive material,such as silver or gold, to form contacts that may be reliably engagedwith connector contacts, i.e. “connectorized.” Referring to FIGS. 21 and22, a module-connector set 500 is shown including a connectorized module515 in exploded view with a mating connector 503 into which the module515 may be removably inserted.

The connector 503 as shown includes a body 518 having side walls 518Bcreating an opening 518C adapted to receive the connectorized module515. Terminals 508 formed, e.g. bends 508B (FIG. 22), to provide apressure fit between a contact area 508A of each terminal 508 and arespective interconnect 511. The terminals as shown may be retained inrecesses 517 in the interior surface 518A of the side walls 518B. Therecesses 517 may provide support to keep the terminals 508 in place andallow the interior surfaces to engage the surfaces of the module 515.The terminals 508 may include a flat portion 508D (FIGS. 22, 23) adaptedfor making a solder connection to surface contacts on a customer circuitboard (not shown). The connector body may include a bottom surface 518Denhancing the structural integrity of the connector walls 518B which aresubjected to the forces exerted by the terminals 508 against theinterconnects 511. The bottom 518D may include openings as shown in FIG.23 through which the terminals may be inserted during assembly of theconnector 503. The bottom 518D may provide electrical insulation betweenthe metal heat sink 502 and the customer circuit board (not shown) onwhich the connector 503 may be mounted. Alternatively, the bottom may bepartially or completely removed to allow better conduction of heat fromthe module 515 out through the customer circuit board. Yet anotheralternative is to use a thermally conductive material in the bottom 518Dof the connector 503. FIG. 24 shows the connectorized module 515inserted into the connector 503.

As shown, the connector terminals 508 exert inward pressure fromopposing ends of the module, however, the contacts may be arranged alonga single side of the module with the connector body providing thenecessary resistive force for the pressure fit. Although theconnectorized module is shown having plated interconnects 511 formingcontacts for engagement with the connector terminals, it should beappreciated by those of skill in the art that many variations arepossible. For example, adapters of the type illustrated in connectionwith FIGS. 15-20 may be used to provide contacts for a hybridconnectorized module allowing other orientations of the module relativeto the connector and to the customer circuit board.

G6. Flush Mount

A flush-mount technique may be used with the horizontal PCB-mountingtechniques discussed above in connection with FIGS. 15-24 to allow thebottom heat sink to come into contact with the customer PCB, e.g. forheat removal. As shown in FIGS. 25 and 26, a through-hole mount module600 is shown adapted for flush-mounting to a customer PCB 900. Themodule 600 as shown includes two through-hole adapters 603A, 603Battached to the singulated module 615. The singulated module 615 may, asshown, have a finned top heat sink 601 and a generally flat bottom heatsink 602 for flush mounting against the PCB 900. Similar to the adaptersdiscussed above in connections with FIGS. 16-20, through-hole adapters603A, 603B have terminals, 608, 609, 610 which include features, such assolder pad 608A, adapted to be attached, e.g. by solder, to respectiveinterconnects on the module 615. The terminals 608, 609, 610 may beadapted to be soldered into through holes 908, 909, 910, respectively,in the customer PCB 900. As shown in FIGS. 25 and 26, the generally flatheat sink 602 may include recesses 602B to accommodate flanges 618B ofthe adapter bodies 618 allowing most of the surface of heat sink 602 torest flush against the surface of the PCB 900. Epoxy or other adhesivemay be used in the recess to secure the adapter body to the module. Therecesses may be an integral feature of the heat sink panel or may beadded at an appropriate point during the manufacturing process,preferably before singulation.

A thermally conductive material 901, e.g. thermal adhesive, may beapplied between the PCB 900 and the module heat sink 602 to facilitateremoval of heat through the PCB 900. Additionally, the PCB surface mayinclude thermally conductive features to conduct heat away from themodule 615. For some applications particularly involving smaller modulesizes, it may be desirable to solder the bottom heat sink 602 to one ormore pads on the PCB 900, in which case the heat sink may include asolderable finish, applied for example by plating. Threaded holes may beprovided, preferably in the flush mount heat sink panel, allowing themodule to be secured using screws to a customer board or cold plate. Theflush-mount modification may allow taller heat sink fins to be used onthe top of the module without increasing the module profile above thecustomer PCB which may provide better thermal management in someenvironments. Additionally, the flush-mount may provide a more robustshock and vibration resistant mechanical solution.

Another flush mount module 650 may include a plurality of pins 661protruding from the bottom heat sink 652 for engagement in through holes911 in the customer mother board 900 as shown in FIG. 25A. Similar tothe flush mount module 600 of FIGS. 25 and 26, the flush mount module650 may include adapters 653A and 653B adapted for making electricalconnections with through holes on the customer mother board 900. Insteadof fins, the top heat sink 651 may include a flat surface to create alow-profile package as shown in FIG. 25A. The pins 661 may be formed asan integral part of the bottom heat sink panel instead of fins.Alternatively, blind holes may be provided in the heat sink panel intowhich the pins may be press fit at any suitable stage of the fabricationprocess. The pins 661 may be used to electrically connect the bottomheat sink 652 to the customer board, e.g. to ground, conduct heat out ofthe module into the customer board 900, and provide mechanical support.The through holes 908, 909, 910, 911 in the customer board may be sizedto provide clearance between the hole and the respective pin tocompensate for any dimensional variations. The pins 661 may optionallyprotrude beyond the bottom surface of the customer board 900 into forcedair along the bottom surface of the board for additional heat removal.Additionally, a heat sink component (not shown) may be fitted onto theprotruding pins to help dissipate heat.

H. Heat Sink Setback

As internal components are reduced in height, e.g. reducing thethickness of the magnetic core, the depth of the interior cavity may bedecreased bringing the heat sink panels closer together, reducing theencapsulant thickness and the resulting module thickness. However,reduction of the encapsulant thickness has the potentially undesirableeffect of reducing the spacing between the electrical interconnects andthe edges of the heat sink panels in the finished module. Whendesirable, e.g. to satisfy safety agency requirements, the separationbetween the exposed interconnects, e.g. interconnects 111, 112, 113, andthe edge of the heat sink, e.g. heat sink 101B, may be increased using asetback, e.g. setback 155, between the edges of the heat sink panels andthe edges of the module 115B as shown in FIG. 10B. The setback 155 maybe created by making wide cuts through the heat sink panels 121, 122along the singulation lines prior to singulation. The wide cutspreferably extend through the heat sink material, e.g. aluminum, andpartially into the encapsulation material to form channels 128A and 129Ain the panel assembly 120A as shown in FIGS. 9B and 9C. If machinedwhile the assembly is still hot from the encapsulation process, thechannels 128A and 129A may be used to divide the heat sink panels intosingulated module dimensions reducing stresses due to differentialcontraction between the heat sink and the encapsulant due to differencesin thermal coefficients of expansion while the panel assembly cools.Stresses on the narrow saw may also be reduced by eliminating the heatsink metal through which the saw must cut during singulation as a resultof the channels 128A, 129A.

I. Process Efficiencies

Using interconnection features that may be exposed during singulationallows the PCB panel 124, containing a plurality of modules, to bemolded as a single unit. Providing embedded interconnects along theperimeter of the circuit that occupy little or no PCB surface area helpreduce wasted PCB area that would otherwise be cut away, allowing closeto full utilization of the PCB for product which may save on cost.Encapsulating the PCB panel with the heat sink panels simplifies thestructural aspects of the modules. Using interior contours in the heatsink to match component heights helps reduce the amount of moldingcompound required for encapsulation. Furthermore, controlling thedistance between the magnetic cores and the internal surface of the heatsink can be used as an alternative to and eliminating the complicationsof the exposed core molding process described in the Exposed CoreApplication.

Furthermore, using the mold panels to form the mold cavity forencapsulating the PCB panel helps free the molding equipment fromproduct specific requirements that may otherwise require customizedmolds, allowing a single piece of molding equipment to be used for awide variety of product mixes. The finished products, e.g. modules 115made using a standard panel size, may have diverse dimensions not onlyin the lateral (length and width) directions, but also in the vertical(thickness) direction (e.g. due to heat sink fin height or componentthickness). However, because the lateral panel dimensions remain thesame, and variations in thickness from panel to panel may beaccommodated by the molding press, the same general purpose moldingequipment may be used for a wide variety of products of diversedimensions. Using power converters as an example, the same mold pressmay be used to encapsulate panels of power converters ranging in (1)footprint size from full size, to half, to quarter, to eighth size (orany other size), and in (2) thickness (height), and in (3) topology,e.g. isolated DC-DC regulating converter, non-isolated buck regulator,DC transformer, etc. to produce a large mix of products.

A panel molding manufacturing process for a mix of products may includesome or all of the following steps. Select a specific product to build.Select the requisite blank heat sink panels, e.g. based upon finorientation, spacing, and height for the specific product.Alternatively, machine the exterior of the heat sink blank panels toproduce the requisite external surface (heat sink surface, mountingfeatures such as threaded holes, fin orientation, thickness, andspacing). Machine the interior surfaces of the heat sink blanks to formthe recesses and other features (i.e. the contours of interior cavity tomatch some or all component locations, size, and height), of thefinished heat sink panels required for the specific product, preferablyunder computer control. Select the appropriate PCB panel for thespecific product. Select and assemble the magnetic cores and othercomponents onto the PCB panel, e.g. by surface mount soldering, etc.Dispense a measured quantity of molding compound into the bottom heatsink panel. Press the bottom side of PCB panel up against bottom heatsink panel. Dispense a measured quantity of molding compound on the topside of the PCB panel. Press top heat sink panel into place on the PCBpanel. Place the panel assembly on a rotary table away from the axis ofrotation, preferably a large distance from the axis, and spin the rotarytable and panel assembly to evacuate air bubbles in the interior cavityto achieve essentially void free fill of panel assembly with moldingcompound. Cure the molding compound. Cut the panel along the cut linesfor singulation. Apply a conformal coating to protect the interconnects,or plate the interconnects, or attach a lead frame, motherboard, orconnector to the exposed interconnects.

J. PCB Symmetries

The components may be symmetrically arranged on the PCB such as shown inthe power converter example of FIG. 27. The top 104-2 and bottom 104-1faces of a populated PCB 104 from an individual power converter moduleare shown in plan view in FIG. 27. The populated PCB 104 is shownrotated along the vertical axis 27 in FIG. 27 to show the symmetry ofthe components.

J1. Symmetrical Distribution Between PCB Surfaces

Many of the larger components may be distributed equally between bothfaces of PCB 104 as shown in FIG. 27. For example, the four input fieldeffect transistors (FETs) 132-2D, 132-2E, 132-1D, 132-1E are shownequally distributed between the top 104-2 and bottom 104-1 surfaces withtwo FETs on each surface. Similar equal distribution between the top104-2 and bottom 104-1 surfaces of the PCB 104 are shown for the eightoutput FETs 132-2B, 132-2C, 132-1B, 132-1C with four output FETs on eachsurface; the twelve input capacitors, 132-2F, 132-2G, 132-1F, 132-1G,with six input capacitors on each surface; and twenty four outputcapacitors 132-2A, 132-1A with twelve output capacitors on each surface.Some of the FETs can function as switches. Distributing largercomponents between the two surfaces of the PCB may decrease stresses onthe PCB, e.g. due to differences in the coefficient of expansion of theencapsulant, e.g. while curing, which may improve the co-planarity andmechanical integrity of the device.

J2. Symmetrical Distribution on a PCB Surface

On each surface of the PCB, components having similar characteristics,such as size or in-circuit power dissipation, may be arrangedsymmetrically for example as shown in FIG. 27 with respect to horizontalaxis 28. It can be seem that relative to the horizontal axis 28, whichis drawn longitudinally through the midline of the top and bottomsurfaces of PCB 104, many of the components are arranged symmetrically.For example, the six input capacitors 132-1F and 132-1G on the bottomsurface 104-1 are symmetrically distributed in a mirror-imagerelationship to each other relative to longitudinal midline axis 28. Thesame basic mirror image relationship is true for the six inputcapacitors 132-2F and 132-2G on the top 104-2 surface of the PCB.Similarly, the mirror image relationship is shown for the followingpairs of components: bottom-side input FETs 132-1D and 132-1E, topsideinput FETs 132-2D and 132-2E, bottom-side output FETs 132-1B and 132-1C,topside output FETs 132-2B and 132-2C and also within the bottom-sideand top-side banks of output capacitors 132-1A and 132-2A.

Distributing larger components symmetrically on a surface especiallywith respect to the longitudinal axis of the PCB may also decreasestresses on the PCB, e.g. due to differences in the coefficient ofexpansion of the encapsulant, e.g. while curing, which may also improvethe mechanical integrity of the device. Additionally, spreading thecomponents out symmetrically on each surface helps to spread the heatproduced by power dissipating devices using a greater surface area forheat extraction improving the thermal performance.

J3. Symmetrical Footprints Between PCB Surfaces

In addition to being equally distributed between the top and bottomsurfaces and being symmetrically distributed on each PCB surface, thecomponents may also be situated such that pairs of components (whereineach component on one surface has a respective counterpart on the othersurface) may be arranged to occupy essentially the same space on thePCB, i.e. a component may occupy a space on one surface thatsubstantially overlaps with the footprint of a component on the othersurface. For example, input capacitors 132-1F on the bottom surface arein the same position as their counterparts 132-2F on the top surface,i.e. they share the same footprint on the PCB. The same relationship isgenerally true for: input capacitors 132-1G and 132-2G; outputcapacitors 132-1A and 132-2A; input FETs 132-1D and 132-2D; input FETs132-1E and 132-2E; output FETs 132-1B and 132-2B; output FETs 132-1C and132-2C; in which the pairs of components occupy the same basicfootprint, albeit on opposite surfaces, of the PCB. One benefit ofsharing footprints allows the pair of components to share a common setof conductive vias used to electrically connect the components on thePCB surfaces to internal conductive layers, e.g. used to form thewindings of the transformer. Because each via is used for bothcomponents in the pair, the total number of vias for making connectionsto the pair of components may be reduced (by as much as a factor of two)increasing the area of conductive layers useable for making connectionsand thus reducing resistance. For example, assuming 6 vias are requiredfor each output FET (a total of 12 vias for two FETs), using symmetricalfootprint approach, the pair of FETs can share the same 6 vias (withoutincreasing the via resistance) and because the number has been reducedthe useable area for conductors may be increased. Alternatively, whilereducing the total number of vias from 12 to some intermediate number,e.g. 8, the resistance of the vias may be decreased because of theincrease in effective vias per FET while still increasing the areauseable for conductors.

J4. Symmetrical Power Dissipation Between PCB Surfaces

The components may be arranged between the PCB surfaces according toheat dissipated during operation. For example, the heat dissipativecomponents may be arranged in a manner that distributes the heat evenlybetween the two PCB surfaces allowing heat produced by power dissipatingdevices to be extracted from both surfaces of the PCB improving thethermal performance. This type of heat dissipation symmetry is alsofactored into the component layout shown in the power converter of FIG.27. For example, two input cells each using the same basic circuittopology are shown, one above and another below axis 28. As shown, thecomponents of each input cell occupy both sides of the PCB in observanceof other factors influencing component layout such as winding locations,etc. In this example, the upper input cell includes the two input FETs132-1D and 132-2D, and the six input capacitors 132-1F and 132-2F. Thelower input cell includes the two input FETs 132-1E and 132-2E, and thesix input capacitors 132-1G and 132-2G. To ensure heat dissipationsymmetry between the two surfaces, the cells may be arranged in mirrorimage layouts as shown. In FIG. 27, input FET 132-2E (top surface) inthe lower cell corresponds to input FET 132-1D (bottom surface) in theupper cell. Similarly, lower cell input FET 132-1E (bottom surface)corresponds to upper cell input FET 132-2D (top surface). As can beseen, the significant power dissipative components of the input cellsare arranged to have one component of one cell mounted on one surfacewith the respective component from the other cell mounted on the othersurface. This type of symmetry may be seen in FIG. 27 with lower cellcomponent 132-2H mounted on the top surface and the respective uppercell component 132-1H mounted on the bottom surface. In some examples,the FETs are arranged such that during operation, the power FETs on thetop surface dissipate power at a level that is comparable to the levelof power dissipated by the power FETs on the bottom surface. Also, thelevel of power dissipated by the power FETs in the upper input cell iscomparable to the level of power dissipated by the power FETs in thelower input cell. For example, the level of power dissipated by thepower FETs on one surface is less than 150% of the level of powerdissipated by the power FETs on the other surface. The level of powerdissipated by the power FETs in the upper cell is less than 150% of thelevel of power dissipated by the power FETs in the lower cell, and viceversa.

Laying out the components using any or all of the above symmetriesproduces several key benefits including, enhanced thermal performance,reducing top to bottom and side to side imbalances during encapsulationcaused by asymmetrical distribution of components may enhance theco-planarity and structural integrity, and shared component footprintson top and bottom PCB surfaces may help reduce conduction losses andincrease efficiency.

K. Center Plate Panel Assembly

In an alternate embodiment, an optional center plate 727 may be usedbetween the top 721 and bottom 722 heat sink panels as illustrated inFIG. 28 through FIG. 32. The center plate 727, which may be made fromaluminum, a molded high temperature plastic or any other materialsuitable for the molding process, includes an opening 729 in which thepopulated PCB panel 724 may sit during the panel molding process. Asshown in the side view of FIG. 29 and the cross-sectional view of FIG.32, the PCB panel 724 may sit entirely within the opening 729 and mayhave some high profile components, such as magnetic cores 131 andcapacitors 132 (continuing with the power converter example), extendingbeyond the planar surfaces of the center plate. The recesses formed inthe interior surfaces of the heat sink panels 721, 722 (described above)may accommodate portions of the components extending beyond the centerplate surface. Conversely, protrusions from the interior surface of theheat sink panels may be used to reduce the distance between the heatsink and lower profile components. However, it may be preferable forease of fabrication and tolerance control to avoid protrusions of theheat sink beyond the surface of the center plate which may put an upperlimit on the thickness of the center plate in some embodiments.

As shown in the exploded perspective view of FIG. 28 and the top planview of FIG. 31, registration features may be provided in the centerplate 727. For example, registration pins 728 may mate withcorresponding holes 734 in the PCB 724 to establish the horizontalposition, i.e. in the X and Y directions, of the PCB relative to thecenter plate 727. Additional registration features such as theillustrated horizontal shelf 728A (FIG. 28), may be provided toestablish the vertical position, i.e. in the Z direction, of the PCBrelative to the center plate. The registration pins 728 may be longenough to extend beyond the upper surface of the PCB panel 724 in theupward direction and beyond the horizontal shelf in the downwarddirection to mate with holes (analogous to holes 152 and 153 in FIG. 4B)which may be provided in the top and bottom heat sink panels 721, 722establishing the horizontal positions of the mold panels relative to thecenter plate 727. Provision of the registration features in the centerplate may help relax certain precision requirements, the complexity, andthus the cost of the heat sink panels.

A cross-section of the panel assembly 720 closed in a mold press takenthrough line 32-32 in FIGS. 30 and 31 is shown in FIG. 32. As shown, theupper mold press 761 engages the center plate 727 directly along itsperimeter in regions 768 and engages the heat sink panels directly alongtheir perimeters in regions 769. Preferably the mold press includesrecessed surfaces 766 providing cavities 765 large enough to accommodatea full range of fin heights (or other heat sink panel features)supporting a diverse range of products. To compensate for dimensionaldifferences between the thickness of the heat sink panels in regions 769and the difference in elevation between interface regions 768 and 769 inthe mold press, one or more compressible features may be provided at theinterface between the heat sink panels 721, 722 and the center plate727. For example, a small crushable feature 723 may be formed along theperimeter of and as an integral part of the heat sink panels asillustrated in FIG. 32. Alternatively a gasket may be used between thecenter plate and one or both of the heat sink panels. As the presscloses on the panel assembly 720 the crushable features 723 arecompressed until the press is closed securely against both the centerplate 727 and the heat sink panels 721, 722. As shown in FIG. 31, thecrushable features may extend along the perimeter of the interior cavityforming a seal between each heat sink panel and the center plate.

The center plate may preferably include an extension, e.g. extension730, to at least one side of opening 729 providing space for one or morechambers 725 as shown in FIGS. 30, 31, and 32. During the transfermolding process, encapsulation material may be forced from the chambersthrough one or more channels 726 (as shown in FIGS. 28 and 32) in thecenter plate into opening 729 and thus the cavity in which the populatedPCB panel 724 is enclosed. An example of encapsulant flow through achamber 725, channel 726, and into the interior cavity 746 isillustrated by the arrows 767 shown in FIG. 32.

In the center plate panel mold assembly, the top and bottom mold panels(i.e., heat sink panels 721, 722) close against the center plate insteadof each other, reducing the thickness of the top and bottom mold panels,increasing the symmetry between, and reducing the complexity of, the topand bottom heat sink panels 721, 722, potentially simplifying themolding press, eliminating critical tolerance accumulations in theassembly, simplifying the process and reducing cost. For example,provision of the chambers 725 and conduits 726 in the center plate 727eliminates the need for sealing along a second axis, e.g. in ahorizontal direction and allows for use of a simpler cull-on-platemolding press. Critical tolerances are reduced to the one verticaldimension of the heat sink panels which can be relaxed using a crushablefeature or a compliant material on the surface that interfaces with thecenter plate. Additionally, the center plate 727 may be standardizedallowing a single configuration to be used with a large variety of heatsink panels such that the center plate may be cost-effectively molded.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, non-metallic mold panels may be used. The center plate may beprovided as a single-use consumable or may be modified to be used as areusable fixture in the molding process. The center plate may beprovided with or without the encapsulation channels. The registrationholes in the heat sink panels may extend completely through the heatsink panels similar to hole 152 shown in FIG. 4B and the registrationpins, e.g. pins 728 (FIGS. 28 and 31), may extend completely througheach of the heat sink panels allowing fasteners to be used inconjunction with the pins to hold the panel assembly together before andafter the encapsulation process. The fasteners may function as or beused in conjunction with a seal around the pin to contain anyencapsulant. Throughput through the mold press may be increased by usingpanel assemblies that are secured together and removed from the moldpress before the panel has cooled or the encapsulant has set or both.The registration pins 728 and corresponding holes 734 may be used toalign the panel assembly during the singulation process. In someexamples, a panel assembly (e.g., 120) may be formed by dispensingencapsulant into a bottom panel mold (e.g., heat sink panel 122),assembling a substrate (e.g., PCB panel 124) into the bottom panel mold,dispensing encapsulant onto a top of the substrate, and assembling a toppanel mold (e.g., heat sink panel 121) onto the substrate. In someexamples, the surfaces of the PCB panel 124 may have conductive featuresthat are covered by an insulative layer. Blank mold panels may bemachined to provide some or all of the various features described abovein an on-demand manufacturing system.

In some examples, the upper and lower heat sinks 121, 122 are clampedtogether by the upper and lower mold presses 161, 162 at respectiveclamp regions of the upper and lower heat sinks 121, 122. The clampregion of the upper heat sink 121 can be located at points along acircumference of an internal cavity defined by the interior surface ofthe upper heat sink 121. The clamp region of the lower heat sink 122 canbe located at points along a circumference of an internal cavity definedby the interior surface of the lower heat sink 122. In some examples,the clamp regions are cut away from the panel assembly 120 to expose theinterconnects 111, 112, and 113. After the cut, portions of the upperand lower heat sinks 121, 122 near an active circuit area remainattached to the panel assembly 120, allowing heat from the activecircuit area during operation to be dissipated through the remainingportions of the upper and lower heat sinks 121, 122. The active circuitarea can be, e.g., an area of the PCB panel 124 having activecomponents, such as magnetic core structures 131 and electroniccomponents 132. Interlocking contours, other than the undercuts 148shown in FIGS. 6, 7, and 12, can also be formed in the interior surfaceof the mold panel, the contour being filled with cured mold compoundenhancing the structural integrity of the singulated module. In someexamples, most of the large-footprint components (e.g., 132-2D, 132-2E,132-2B, 132-2C) are distributed substantially symmetrically betweenquadrants surrounding the transformer core (e.g., 131-2) on a surface ofthe PCB panel 124. For example, in FIG. 27, the input FETs 132-2D and132-2E are distributed substantially symmetrically between theupper-right and lower-right quadrants surrounding the transformer core131-2. The output FETs 132-2B and 132-2C are distributed substantiallysymmetrically between the upper-left and lower-left quadrantssurrounding the transformer core 131-2.

Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. An apparatus comprising: a power converterincluding a printed circuit board (“PCB”) comprising a plurality ofconductive layers and having a top surface and a bottom surface; amagnetic core structure magnetically coupled to a winding formed bytraces in one or more of the conductive layers in the PCB; and aplurality of power semiconductor devices, a first set of the powersemiconductor devices being mounted on the top surface and electricallyconnected to dissipate power at a level, Pt, during operation of theconverter, a second set of the power semiconductor devices being mountedon the bottom surface and electrically connected to dissipate power at alevel, Pb, during operation of the converter; wherein the powersemiconductor devices are distributed between the first and second setsto distribute heat generation during operation of the converter suchthat each level Pt, Pb is less than 150% of the other level Pb, Pt. 2.The apparatus of claim 1 wherein a plurality of the power semiconductordevices in the first set are each positioned in a location on the topsurface substantially overlapping a location on the bottom surfaceoccupied by a power semiconductor device in the second set.
 3. Theapparatus of claim 1 wherein the power semiconductor devices areelectrically connected using a respective set of conductive vias in thePCB, and a plurality of the power semiconductor devices in the first setshare their respective sets of conductive vias with corresponding powersemiconductor devices in the second set.
 4. The apparatus of claim 2wherein the power converter further comprises circuitry including a pairof cells having a common circuit topology and each including powersemiconductor switches from each of the first and second sets; each cellhaving its respective components arranged in a pattern, wherein thepattern of components of one cell is substantially a mirror image of thepattern of components in the other cell.
 5. The apparatus of claim 4wherein a component from one of the cells is located on an oppositesurface of a respective component from the other one of the cells. 6.The apparatus of claim 5 wherein the cells comprise input cells.
 7. Theapparatus of claim 3 wherein the power semiconductor devices compriseoutput switches.